[Python-Dev] Adding types.build_class for 3.3

[Mark Shannon]

Nick Coghlan wrote:
> On Wed, May 9, 2012 at 4:37 PM, Daniel Urban <urban.dani+py at gmail.com> wrote:
>> On Wed, May 9, 2012 at 3:10 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
>>> We need the explicitly declared metaclass as well as the bases in
>>> order to determine the correct metaclass.
>> Note, that the current patch (at http://bugs.python.org/issue14588)
>> obtains the explicitly declared metaclass from the keywords dict
>> (exactly like the class statement).
> 
> Ah, good point. In that case, consider me convinced: static method it
> is. It can join mro() as the second non-underscore method defined on
> type().
> 

Be careful adding methods to type. Because type is its own metaclass 
descriptors can appear to add strangely:

int.mro()

[<class 'int'>, <class 'object'>]

type.mro()

Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: descriptor 'mro' of 'type' object needs an argument

As a consequence of this, making build_class either a class method or a 
static method will cause a direct call to type.build_class() to fail as 
neither class method nor static method are callable.

Cheers,
Mark.